(Portland, Oregon) – The International Space Station made quite the spectacular run over Portland one day in early June at twilight, zipping over Beaverton/Hillsdale Highway on the border between Portland and Beaverton about 9:38 p.m.

These photos were taken not far from the Oregon Coast Beach Connection office in Portland on June 6. It shows up here as streaks of light, with exposures ranging between two to eight seconds.

The ISS came over at a magnitude -3.3 – the measure of degree of brightness. Checking the schedule of Portland fly-overs, this was actually among the brightest of the visits. (Above: the station begins rising from the SW towards the NE)

As the astronomy website Heaven's Above defines it:

“The lower the value, the brighter the object, so magnitude -4 is brighter than magnitude 0, which is in turn brighter than magnitude +4,” the website says. “The scale is logarithmic, and a difference of 5 magnitudes means a brightness difference of exactly 100 times. A difference of one magnitude corresponds to a brightness difference of around 2.51 (the fifth root of 100).”

The method of measurement goes all the back to the ancient Greeks, who divided stars into six different categories for brightness. The stars of the first magnitudes, they decided, were the ones first visible after sunset.

This is a measure of the brightness of a celestial object. The lower the value, the brighter the object, so magnitude -4 is brighter than magnitude 0, which is in turn brighter than magnitude +4. The scale is logarithmic, and a difference of 5 magnitudes means a brightness difference of exactly 100 times. A difference of one magnitude corresponds to a brightness difference of around 2.51 (the fifth root of 100).

The system was started by the ancient Greeks, who divided the stars into one of six magnitude groups with stars of the first magnitude being the first ones to be visible after sunset. In modern times, the scale has been extended in both directions and more strictly defined.

Examples of magnitude values for well-known objects are:

The sun is a -26.7, which is about 400 000 times brighter than the full Moon. The full Moon is a -12.7, and the ISS tends to be about a -2.

There are still plenty of chances to see it over Portland and even the Oregon coast between now and June 21 – weather permitting. Some are even at magnitudes close to -3. See the schedule for exact times.